Telephone substation equipment



March 1935. J. w. GOODERHAM El AL 1,993,780

TELEPHONE SUB-STATION EQUIPMENT Filed Feb. 11, 1951 JWGOODERHAMINVE'NTORSI H.7.BUDENBOM (.S.J HNSON I ATTORNEY Federated E2 TELEPHONESUBSTATION EQUIPMENT John W. Gooderham, Larchmont, N. Y., and Horace T.Budenbom, Short Hills, and Kenneth S. Johnson, South Orange, N. .J.,assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y.,a corporation of New York Application February-11, 1931, Serial No.514,930

2 Claim.

This invention relates to telephone systems and particularly tosubscribers substation equipment employed in the establishment ofautomatic telephone connections.

With the advent of radio broadcastingand its ever increasing popularitywith the radio public there has been a demand for radio reception whichis free from local controllable disturbances. It is a well known factthat the development of radio receivers has not reached the stage wherethey, of themselves, embody means for minimizing the objectionableeffects caused by local static which is set up by neighboring electricalapparatus.

Among the types of electrical apparatus which have been found to createa condition which manifests itself in'radio receivers in the form oflocal static is the telephone dial. In manipulating a telephone dial totransmit impulses to prepare automatic telephone switches for thecompletion of a telephone connection, a current carrying circuit isinterrupted intermittently a number of times in accordance with thesettings of the dial.

' These interruptions eflected by the dial mechanism produce electricalsurges which are picked up by neighboring radio receivers and reproducedtherein as clicks or other equally objectionable noises which materiallyinterfere with the reception of broadcast programs.

It is an object of this invention to provide an improved telephonesubstation set which embodies in its structure means for suppressingradio interference caused by the electrical surges set up by themanipulation of the calling dial associated with the set.

This object is attained in accordance with a feature of the invention bythe provision of a filter unit which is permanently associated with thepulsing contacts of the dial associated with the subscriber's set.

Another feature of the invention resides in the small, compact design offilter which readily adapts itself to be permanently located in the baseof a subscribers telephone set and in close proximity with the pulsingcontacts of the calling dial. This is a particularly desirable featurein that housing the filter. unit within the base of the telephone setpermits the use of smaller f lter elements with better suppressionresults .at the source of disturbance, than may be attained by largerelements located elsewhere at the subscribers station.

The preferred form of filter unit employed in this invention comprisestwo elements a condenser and an inductance coil, combined in such amanner as to form a small, compact unit which can be readily mounted ona bracket secured within the base of the telephone set and from whichthe necessary electrical connections with the dial contacts can-beeasily made. The constants of the filter elements are necessarilypredetermined to give the maximum suppression of radio interference andit has been found that the value of inductance of the filter coil is'critical within narrow limits.

Other forms of filter units which are contemplated by this inventionprovide various degrees of suppression and will be described in detailin a later description.

The invention will be readily understood from the following detaileddescription made with reference to the accompanying drawing in whichFig. 1 is a perspective view of a filter unit employed in thisinvention; Fig. 2 is a bottom plan view of a telephone subset with thebase cover remove showing the manner in which the filter unit is-mountedwithin the base and its relative disposition with respect to the pulsingcontacts of the dial mechanism; Fig. 3 is an elevation of a part of atelephone subset with a portion of the base casing broken away exposingthe filter unit; Fig. 4 is a drawing of a substation circuit showing themanner in which the preferred form, of filter is electrically connectedwith the telephone dial; Fig. 5 is a drawing of a substation circuitshowing a modified form of filter; Fig. 6 shows a substation circuitembodying a still further modified form of filter; and Fig. 7 showsanother arrangement of applicants invention in which a two elementfilter located in the base of the telephone handset is employed inconjunction with an inductance coil located in the bell box.

Referring to Fig. 1, the filter elements, namely a condenser and aninductance coil may be combined and enclosed in any suitable manner in acontainer 10 which is provided at one end with a hook-like projection 11which is adapted to fit into and lock in a slot in the bracket 12. Theother end of the container 10 is provided with a projection 13 in whichthere is a hole which accommodates screw 16 by means of which thecontainer is made fast to the bracket 12. If desirable, a resistanceelement may be included in the filter unit and may be incorporated inthe structure of one of the leads 14 and located outside the container.Theother leads 15 are provided for obvious reasons.

The bracket 12 is secured to the underside of the casing of the subsetbase 17 in any suitable manner to which the container 10 of the filterunit is secured by means of screws 16 as hereinbefore described. It isbelieved unnecessary to identify all the apparatus disclosed in Fig. 2as such equipment and its functions are well known to those skilled inthe art. However, as the pulsing contacts -of the dial mechanism aretied up with the present invention, they are identified by the numerals19 and 20.

In Fig. 3 a well known type of dial 21 is shown mounted on the base of astandard type telephone substation handset. By manipulating the fingerwheel of the dial 21, the contacts 19 and 20 are intermittently actuatedto transmit current pulses which control the setting of automaticswitches in the establishment of a telephone connection.

In Fig. 4 the elements which constitute the filter unit are shown at 23and 24 and are respectively, a condenser and an inductance coil. Thesetwo elements are connected electrically in a series circuit which isconnected in shunt with the dialing contacts 19 and 20. In eflect,however, it will be noted that the inductance coil 24 is connected inseries with one of the conductors of the telephone line 25. Theactuation of the dial finger wheel as hereinbefore stated, causesrepeated interruptions of the dialing contacts and as these contacts areconnected across the telephone line 25 with which there is associatedthe usual current source, there are set up at the dial contacts, currentsurges. The filter unit consisting of the condenser 23 and inductancecoil 24 acts to suppress the radio frequency components of these surgesthereby rendering them ineffectire in causing disturbances toneighboring radio receivers without interference with the usual dialpulses which control the setting of automatic telephone switches.

Fig. 5 is similar to Fig. 4 except that the filter unit is shownconsisting of a resistance 28, condenser 2'7 and inductance coil 22.Such a type of filter may be employed in instances where it is essentialto provide protection for the contacts of the dialing mechanism.

In some cases, and particularly where the telephone is locatedrelatively close to the radio receiver, there has been noted anincreased disturbance to radio reception when the dial operator graspsthe handset during dialing. In order to reduce this objectionable effectapplicants have devised a modified form of filter which is shown in Fig.6. In this arrangement, a small condenser 33 is connected at the commonterminal of the filter, that is, at the point where the condenser 30 andinductance coil 31 are electrically Joined. The other side of thecondenser 33 is connected to the frame of the telephone rtet asindicated by the numeral 40, Fig. 6. The insertion of a small capacityat this point has a tendency to balance out the effects caused by thebody of the dial operator. condenser may be housed in the container 10together with the other filter elements and the terminal to be securedto the frame made me- In actual practice the auxiliary weaves chanicallyfast to the inside of the container casing.

Fig. 7 shows a modified arrangement of the filter elements which areemployed in suppressing radio interference caused by the electricalsurges set up by the substation dialing mechanism. In this modificationthe inductance coil 35 is shown located in the bell box of thesubstation equipment while the condenser and resistance element 36 and37 are shown located in close proximity with the dialing contacts,preferably within the base of the telephone handset.

The mounting of the filter unit within the base of the telephone set isa very desirable feature in that it has been determined that by solocating the filter in close proximity with the dialing contacts, thesource of the disturbance, sufiicient suppression of the radiointerference is obtained with considerably smaller filter elements thanis obtained when the elements are located elsewhere at the subscribersstation. The possibility of using relatively small filter elements inturn, renders it possible to confine the filter within a compact,unitary structure which can be readily accommodated in the very limitedspace available in the base of a telephone handset.

From the foregoing it is evident that applicants have not only devised afilter unit which is highly satisfactory in suppressing the interferenceto radio reception caused by the current surges set up by the dialingcontacts of a telephone dial but by so locating the filter with respectto the dialing contacts they have rendered it possible to obtainsufficient suppression with relatively small filter elements whichpermit the filter unit to be made of such dimensions as to permit it tobe mounted in the base of the telephone handset without relocating anyof the other equipment to furnish the necessary mounting space and whichmay be conveniently furnished to telephone sets already in commercialuse.

What is claimed is:

1. In a subscribers subset of the dial type, a filter embodied in thestructure of said subset for suppressing radio interference caused bythe electrical surges set up by the actuation of the dial, and acondenser electrically associated with said filter and having a terminalthereof secured to the frame of said subset for augmenting thesuppression effect of said filter.

2. In combination, a telephone subset having a dial, a bracket locatedwithin the base of said telephone subset, a container housing aplurality of filter elements and having a hook-like projection at oneend which fits into an aperture in said bracket and positionssaidcontainer on said bracket, means for securing the other end of saidcontainer to said bracket and electrical connections between the filterterminals and the dialing contacts of said dial.

JOHN W. GOODERHAM. HORACE T. BUDENBOM. KENNETH S. JOHNSON.

